Akatsuki Venus Climate Orbiter Options

[Paolo]

If Akatsuki was able to enter a kind of orbit around Venus with its smaller
engines, then why did they bother with the larger engine that failed?

the orbit that Akatsuki has entered is not optimal and a few of the scientific objectives have been compromised

[pandaneko]

I can't say for certain that this is the case, but the most obvious reason to me would be the approach velocity and how much Delta-v was needed to reach orbit. Akatsuki approaching Venus direct from Earth required a much bigger VOI burn than the lower-velocity approach late last year.

Thank you for this. Thank you.

P

[JRehling]

No spacecraft has ever entered a close-in circular orbit around another planet without aerobraking. Orbits like that have only been achieved at Venus (Magellan being the only case) and Mars (several cases, but much less planetary mass).

An elliptical orbit with a low periapsis is pretty good for many scientific purposes. Akatsuki, like Venus Express, Mars Express, and all pre-Nineties Mars/Venus orbiters are/were able to get periodic close-ups along with regular global monitoring. Given that Venus doesn't have seasons, it seems like a pretty good option to have a Venus atmosphere observer in an orbit like Akatsuki's, to collect both close-up and global monitoring, although an orbit like that would have drastically compromised the goals of surface-mapping missions like Magellan or Mars Reconnaissance Orbiter.

[pandaneko]

Page-31

Example 5:

(title):

Clarifying atmospheric motions by cloud chasing (UVI+IR1+IR1 (must be 2?, P)+ LIR)

(just below mini image of Venus, above earlier graphic):

Obtained wind velocity distrbution by analysing 3 images (at 365mm and every 2 hours) taken by UVI

(just above wind vector diagram):

Wind velocity distribution in equator region (S Latitude 25 ° -　N Latitude 25 °）

(immediately below wind vector diagram):

Atmospere flows by super rotation, but motion's spatial pattern changes constantly. By analysing, at a number of
different altitudes, we aim to find out what kind of fluid waves exist and how they are related to super rotation, and
how they are responsible for vertical circulation of Venusian atmosphere.

P

[pandaneko]

An elliptical orbit with a low periapsis is pretty good for many scientific purposes.

Thank you for this. "periapsis" and a counterpart to it are the words I should have been using
in some places of my translation. Instead, I always use "nearest Sun"etc etc because I can never
distinguish them and remember which is which.

It took me 15 to 20 years to learn the difference between latitude and longtitude, after all.
So, my excuses...

P

[pandaneko]

Page number of the last translated page shoud be 32, instead of 31.

Page-33

Observation results (summary)

Same as page-10

(After this page there are some more on instruments, mainly. I think I will do them, if not all,
as students may not be that familiar with them)

P

[pandaneko]

Page-36

IR1: 1mm camera

By using 1 mm wave length which enables the camera to see below Venusian clouds down to ground level we aim to:

cloud movements in lower atmosphere, water vapour distribution, mineral composition of ground surface, existence of
active volcanoes etc.

1mm camera IR1

Mass: approx. 6.7kg ※
Field of view: 12°
Detector: Si-CSD/CCD (1024 pixels×1024 pixels)

Observed wave lengths (targets)

1.01 mm （night： ground surface, clouds）
0.97 mm （night: water vapour）
0.90 mm （night: ground surface, clouds）
0.90 mm （day time: clouds）

※ including circuits (approx. 3.9 kg) shared with IR2

P

[pandaneko]

Page-37

IR2: 2mm camera

1. By using wave lengths near 2mm which alow us to penetrate Venusian clouds we aim to obtain basic data for
lower atmospheric circulation and cloud physics via cloud density, cloud nucleus size, and carbon monoxide distribution.

2. By observing, before reaching Venus, zodiacal lights we aim to clarify the behaviour of interplanetary dusts.

2mm camera: IR2

Mass: approx. 18kg ※
Field of view: 12°
Detector: PtSi-CSD/CCD (1024×1024)
Wave length (observation target）

1.735mm （night: clouds and nucleus size distribution）
2.26 mm （night: clouds and nucleus size distribution）
2.32 mm （night: carbon monoxide）
2.02 mm （day time: cloud top altitude）
1.65 mm （Zodiacal lights）

※ including cryos and circuits commmon to IR1 (approx. 3.9kg)

P

[pandaneko]

Page-38

LIR: Mid infra red camera

This camera is meant to capture cloud temperatures using 10mm wave length, thereby clarifying wave motions
at top cloud layers, convection activities, and wind velocity distribution at the night side cloud top altitude.

Mid infra red camera: LIR

Mass: approx. 3.3kg
Field of view: 12.4×16.4°
Detector: unclooled borometer (248×328)
Observed wavelength (target): 10 mm （Day time/night time： cloud top temp.）

P

[pandaneko]

Page-39

UVI: Ultra violet imager

By imaging the distribution of sulfur dioxide responsible for cloud formation and unkown chemical substance
which absorbs ultra violet light and their variations we aim to obtain wind velocity distribution at cloud top levels.

Ultra violet imager: UVI

Mass: approx. 4.1kg
Field of view: 12°
Detector: Si-CCD (1024×1024)
Observed wavelength (target):

283 nm: （daytime： sulfur dioxide at cloud top level）

365 nm: (night time: unknown absorbing substance）

P

[pandaneko]

Page-40

LAC: Lightening and atmospheric light camera

1. By imaging the pale light emitted by oxygen molecules in the upper layer of Venusian atmosphere at around 100km
we aim to visualise the variations in daytime/nightitme circulation and atmospheric wave motion.

2. By high speed exposure of 30,000 times/second (temporal resolution of 32msec) we aim to put a final end end to
ongoing argument about the existence or otherwise of Venusian lightenings.

Lightening/atmospheric light camera: LAC

Mass: approx. 2.3kg
Field of view: 16°
Detector: 8×8 APD matrix array
Observed wavelength (target):

777.4nm: （night： lightenings）
480-650nm: （night： oxygen molecules atmospheric light）
557.7 nm: （night： oxygen atoms atmospheric light）
545 nm （for comparison purposes）

P

[pandaneko]

Page-41

USO: Ultra stable oscillator

This is used for radio wave occultation.

We can gain information about vertically propagating wave motion and thermal structure of Venusian atmosphere
and its temperature variation with altitude by monitoring changes in strength and frequency of the radio waves reaching earth
through Venusian atmosphere.

Ultra stable oscillator: USO

Mass: approx. 2kg
Wavelength :

USO frequency: 38MHz
Transmission frequency: 8.4GHz

Target: Temp., sulfuric acid vapour, electron density

[graphic image: radio wave occultation]

USO is fixed inside the satellite

P

[pandaneko]

In the immediate wake of this year's report I am now on to JAXA's November 2015 report.

There will be some overlapps with this year's and they will be omitted.

Page-1

Circular orbit insertion (plan) and observation scheme of Akatsuki

9 November 2015
JAXA
ISAS project team for Akatsuki


Page-2

Outline

・　Re-insertion of Akatsuki will be attempted on 7 December 2015 (JST).

・　We tried to insert Akatsuki into a circular orbit around Venus on December 2010. That attemt failed due to mul-functioning
of the main engine. Akatsuki is currently flying in an orbit around the sun.

・　The renewed attmpt this time will insert Akatsuki into an elliptical orbit with a higher furthest point from Venus using 4 attitude control
engines without relying on the failed main engine.

・　Mission objective is to continously observe atmospheric motion of Venus and ellucidate on the mechanisms of
its atmospheric circulation.

P

[pandaneko]

Page-3

Mission Objectives

1. Earth and Venus are similar in size and solar radiation inputs are also similar.

2. However, climates are very different. For instance, the high velocity wind (approx. 100m/sec) at the upper layer of
Venusian atmosphere, called "Super rotation", is noticeable.

It is a high velocity wind which goes around Venus in 4 earth days. Venus has a rotation period of approx. 243 days.

3. Why these differences? We want to know.

(On the diagram left globe is earth. Right globe is Venus)

(around earth peripheral):
Character set at 10:00 is Hudley circulation, at 11:00 Ferrell circulation, and at 11:50 Polar circulation.

Character set in upper hemisphere of earth is Westerly, and that near the equator is the trade wind.

Character set in the middle of Venus is Super Circulation, and at the bottom is the Meridian plane circulation.

P

[pandaneko]

Page-4

Mission objective

(above two graphical images)

By examining, 3-dimentionally, the motion of thick Venus atmosphere we wish to clarify the mechanisms controlling the climate
on Venus and compare them with those on the earth.

(graphical images here)
(Satellite graphic not translated)

(There are 9 lines on the lefthand side of this graphics page, all pointing to the image in the middle. Numbering corresponds
to those lines from top to bottom)

1. Temperature/sulfuric acid vapour altitude (radio wave occultation)
2. Atmospheric lights (Lightening and atmospheric camera)
3. Sulfur dioxide (Ultra violet image)
4. Cloud altitude (Mid infra red camera)
5. Lower altitude clouds (1&2 micrometer camera)
6. Wind velocity spectrum (as judged by cloud movement)
7. Carbon monoxide (2 micrometer camera)
8. Lightening discharge (Ligthening and atmospheric light camera)
9. Water vapour (1 micrometer camera)

(and at the very bottom, from left to right)

Ground surface material/active volcanos (1 micrometer camera)
Ground surface

(Character sets on the right hand side (Top to bottom))

3-D observation of thick atmosphere

1. Stratosphere
2. Sulfuric acid clouds
3. Troposphere

(below these two graphical images)

・　Why does the super rotation occur?
・　How does the Meridian rotation affect Venetian climate?
・　How are clouds produced that cover the entire surface of Venus?
・　Can lightenings occur in the atmosphere in which there are no ice crystals?
・　Are there active volcanoes?

P